Can a vet actually do this?

[Kovarr]

A friend of mine has a cat, who is very ill. The cat has some condition (I'm sorry, I can't remember the name) where it isn't eating. At all. Or drinking. The cat is on prednasone, a heartburn-type medicine, and something for neasua (sorry for spelling). The cat seems to be allergic to fish, so any tuna is out. She has tried chicken, beef, even broth to get it to drink. Nothing. The cat seems to have energy (will chase spiders) and still grooms, and is affectionate, but it's an indoor cat, so she knows it's not eating.

She is going through university, and can't afford to keep her cat on these medicines all the time. (And PLEASE don't say she shouldn't have gotten the cat if she didn't have the money to look after it. It's a rather dumb point of view, and when she DID get the cat she was working, but lost her job, so is being sponsored to go to University). She has talked to the vet about putting the cat down, and the vet refuses, because the cat is not "in intolerable pain". My friend says the cat has not improved in a long time, is still losing weight. She knows that soon there will be a time when the meds run out and she can't afford more. She doesn't WANT the cat to be in "intolerable pain". So here is my question:

Can a vet actually refuse to put an animal down if it is currently healthy, but has a condition, and the owner has explained that once these meds are gone, she can't afford more? Where I live, our vet will put an animal down under those conditions, so I'm confused that this vet is basically saying, "No, your cat really has to suffer before I will condone you putting it down". Can he do this?